Method for preparing carboxylic acids by palladium carbonylation

ABSTRACT

The present invention relates to a process for the preparation of β- or γ-unsaturated or saturated carboxylic acids. 
     It relates more particularly to the hydroxycarbonylation of an organic compound comprising a conjugated unsaturation, such as butadiene, by the action of carbon monoxide and water in the presence of a palladium-based catalyst. The carboxylic acids thus obtained are preferably pentenoic acids. According to the invention, the reaction medium after the end of the hydroxycarbonylation stage is treated with hydrogen to reduce the palladium present in the 2+ oxidation state to palladium in the zero oxidation state and the precipitated palladium is recovered.

The present invention relates to a process for the preparation of β- orγ-unsaturated or saturated carboxylic acids.

It relates more particularly to the hydroxycarbonylation of an organiccompound comprising a conjugated unsaturation, such as butadiene, by theaction of carbon monoxide and water in the presence of a palladium-basedcatalyst. The carboxylic acids thus obtained are preferably pentenoicacids.

One of the possible routes of access to adipic acid, which is one of thetwo basic constituents of polyamides, such as polyamide 6,6, is thedouble carbonylation of butadiene or its derivatives.

Although it is possible to imagine carrying out the twohydroxycarbonylations leading from butadiene to adipic acid in a singlestage, it turns out in practice that the two reactions have to becarried out successively if it is desired to obtain selectivities whichare sufficiently high to be able to envisage an economically viableindustrial process.

U.S. Pat. No. 3,509,209 discloses the hydroxycarbonylation of variousolefins, including butadiene, by carbon monoxide and water in thepresence of hydrochloric acid or hydrobromic acid and of apalladium-comprising catalyst at a temperature of 15° C. to 300° C. andunder a pressure of 1 to 1 000 bar, preferably of 10 to 200 bar.

Under the conditions described, it is observed that the yields ofpentenoic acids are very low and that, in reality, the product obtainedis very often valerolactone.

Patent FR-A-2 529 885 has provided a process for the preparation of β-or γ-unsaturated acids, such as pentenoic acids, by carbonylation of aconjugated diene (more particularly butadiene) in the presence of water,of a hydrohalic acid, of a palladium-based catalyst and of a quaternaryonium salt, the onium being that of an element chosen from nitrogen,phosphorus and arsenic.

This process gives good results but it requires the use of a relativelylarge amount of a quaternary onium salt, which is an expensive compoundand one whose presence is of such a nature as to complicate thetreatment of the mixtures at the end of the reaction.

European Patent 0 648 731 also discloses a process for thehydroxycarbonylation of butadiene and its derivatives to pentenoic acidsin the presence of crotyl chloride, in the proportion of at least twomol per mole of palladium, the palladium being at least partially in theform of a π-crotyl complex. This process makes it possible to avoid theuse of onium salt.

These various processes make possible the manufacture of carboxylicacids with acceptable yields and selectivities. However, the recoveryand the recycling of the catalyst has never been described in thesedocuments. As the metal used is a precious metal, the partial recoveryof this catalyst does not allow an industrial development of theseprocesses.

One of the aims of the present invention is to provide ahydroxycarbonylation process comprising a complete or substantiallycomplete recovery of the palladium catalyst. Furthermore, the inventionprovides a recovery of the palladium which makes possible recycling ofthe latter in a further hydroxycarbonylation stage.

To this end, the invention provides a process for the manufacture of β-or γ-unsaturated carboxylic acids or of saturated carboxylic acids byreaction, with carbon monoxide and water, of a compound comprising anethylenic or acetylenic unsaturation conjugated with anotherunsaturation or an electron-donating group carried by the carbon in theposition α to the said unsaturation. This reaction is carried out in thepresence of a palladium-based catalyst which is soluble in the medium.

The process of the invention is characterized in that the reactionmedium, at the end of the hydroxycarbonylation reaction, is treated in afirst stage, in order to extract the carbon monoxide present in themedium by evaporation or entrainment of the CO, and then in a secondstage, in order to reduce the palladium present in the medium topalladium in the zero oxidation state by treatment with hydrogen. Thepalladium thus reduced precipitates and can be separated from thereaction medium by conventional solid/liquid separating means.

According to one characteristic of the invention, the concentration ofCO in the medium before treatment with hydrogen is advantageously lessthan 600 ml of CO per litre of solution, preferably less than 100 ml ofCO per litre of solution. The concentration of CO is also preferablygreater than 0.001 ml of CO per litre of solution.

The term “compounds comprising an unsaturation” should be understood asmeaning the compounds of general formulae:

in which the carbon in the α position with respect to the ethylenic oracetylenic unsaturation also carries an ethylenic unsaturation or anelectron-donating radical, such as, for example, halogen atoms,substituted or unsubstituted amino groups, or alkoxy, hydroxyl, oxo,epoxy, carbonyl, mercaptoalkyl, ester and/or cyano groups.

Mention may be made, as examples of such unsaturated compounds, ofdiolefins, allyl alcohols, allyl ethers, allyl esters and allyl halides.

The preferred compound of the invention is butadiene, which makespossible the manufacture of pentenoic acids by simplehydroxycarbonylation or adipic acid by double hydroxycarbonylation.

The catalyst of the invention is a palladium compound which is solublein the reaction medium. The compounds for the implementation of theinvention are those described in the documents cited above to illustratethe state of the art.

Mention may be made, for example, of palladium compounds comprising oneor more anionic groups, such as, for example, those derived fromhydrochloric, hydriodic, hydrofluoric or hydrobromic acids, sulphuricacid, nitric acid or carbonic acid.

Anionic groups derived from sulphonic acids, thioalcohols or carboxylicacids, such as acetic acid, propionic acid or pivalic acid, or the like,are also suitable.

Use may also be made of complexes formed from compounds comprisingphosphorus or nitrogen atoms.

The palladium can also be present in the form of organic complexes,which can be formed before the introduction into the reaction medium ordirectly in the said medium.

Examples of complexes which can be used in the present process are:bis(π-allylpalladium chloride), bis(π-allylpalladium bromide),acetylacetonato(allyl)palladium, bis(π-isobutenylpalladium chloride),bis(π-cyclohexenylpalladium chloride) and other π-allyl complexes, suchas bis(π-4-chlorocrotylpalladium chloride) andbis(π-2-methyl-4-chlorocrotylpalladium chloride),π-allylcarbonylpalladium chlorides and π-isobutenylcarbonylpalladiumchloride, respectively, for example (C₄H₇Pd₂Cl₂CO)₂), and, furthermore,ethylenepalladium chloride.

It is also possible to use organic palladium complexes, such aspalladium acetylacetonate, bis(bibenzylideneacetone)palladium, the dimerof palladium crotyl chloride, or complexes of aromatic or aliphaticphosphines with palladium, such as tetrakis(triphenylphosphine)palladiumor bis(triphenylphosphine)palladium dichloride.

According to a preferred embodiment of the invention, the palladiumcatalyst is formed in situ by addition of crotyl chloride, in aproportion of at least two mol per mole of palladium. The palladium isthus at least partially in the form of a π-crotyl complex, as disclosedin European Patent No. 0 648 731.

According to the invention, the process for the hydroxycarbonylation ofunsaturated organic compounds described above, which compounds will beexemplified for more clarity with reference to butadiene, by carbonmonoxide and water is advantageously carried out at a carbon monoxidepressure greater than atmospheric pressure.

Advantageously, the water present in the reaction medium represents anamount of less than or equal to 20% by weight with respect to the weightof the reaction mixture.

The term “butadiene derivative” is understood to mean, in the presenttext, in particular allylic butenols, such as 3-buten-2-ol, 2-buten-1-oland their mixtures, or addition compounds of hydrogen chloride withbutadiene (chlorobutenes), the main one of which is crotyl chloride.

In the present process, it is possible to employ butadiene, one or moreof its derivatives or mixtures of butadiene with one or more of itsderivatives. Butadiene or mixtures predominantly comprising butadienerepresent, however, the preferred substrates.

The π-crotylpalladium complex catalyst can be introduced into thereaction medium or can be formed in situ from Pd halides, moreparticularly the chloride, from Pd carboxylates, in particular theacetate, or from finely divided palladium metal.

The amount of π-crotylpalladium catalyst used in the process can varywithin wide limits. Generally, from 10⁻⁵ mol to 0.2 mol of Pd isemployed per mole of butadiene or of butadiene derivative charged to thereaction and preferably from 10⁻⁴ mol to 0.1 mol per mole.

In addition to the π-crotylpalladium catalyst, palladium can also befound in the reaction medium in another less active form (for example,Pd metal or Pd chloride) in a variable amount. In an industrial process,it is, however, preferable for all or virtually all the palladium to bein an active form which is soluble in the medium, such asπ-crotylpalladium, optionally with palladium chloride.

The π-crotylpalladium complex can be prepared, for example, by reactinga palladium salt, such as palladium chloride, with crotyl chloride in asolvent which can be composed of a water/methanol mixture. The mixtureis stirred, generally at ambient temperature, advantageously under agentle stream of carbon monoxide. The π-crotylpalladium complexprecipitates. After an optional degassing phase, the mixture is pouredinto water and is then extracted using a suitable organic solvent, suchas, for example, chloroform. The complex is subsequently isolated fromthe organic solution by evaporation of the solvent.

The crotyl chloride promoter may be introduced into the reaction mixtureor can be formed in situ from butadiene and/or 2-buten-1-ol andhydrochloric acid.

It preferably represents, as mole per mole, from 5 to 10 times theamount of palladium, although it can be present in larger proportions,since it can constitute all or part of the substrate to behydroxycarbonylated.

Taken as a whole, it is preferable to have, in the reaction medium, aCl/Pd molar ratio of less than or equal to 100 and preferably of lessthan or equal to 20, as high ratios have a harmful effect on thekinetics of the reaction.

As indicated above, the concentration of water in the reaction mixtureis advantageously maintained at a value equal to or less than 20% byweight with respect to the weight of the said mixture. This is becausethe concentration of water has an effect on the kinetics of thereaction. This concentration of water will preferably be maintained at avalue of equal to or less than 8% by weight and more preferably still ata value of equal to or less than 5%.

As water is an essential reactant in the hydroxycarbonylation reaction,an advantageous alternative form of the process of the inventionconsists in injecting this water as the reaction progresses, which makesit possible to maintain its concentration in the reaction mixture at avery low value while making it possible for the reaction to be carriedout.

Although the presence of a third solvent is not excluded, the reactionis generally carried out without a solvent other than the reactantsthemselves or the reaction products. It can also be favourable tointroduce, from the beginning of the hydroxycarbonylation reaction, apentenoic acid and more particularly penten-3-oic acid, in order tominimize side reactions.

In the context of an industrial implementation of the process,operations in which the unreacted butadiene is recycled can lead to theintroduction, into the reaction medium, of more or less significantamounts of other compounds, in particular byproducts formed during thehydroxycarbonylation reaction. Thus, it is possible to have, in thereaction mixture, butenes, γ-valerolactone, valeric acid, adipic acid,2-methylglutaric acid, 2-ethylsuccinic acid, 2-methylbutanoic acid or2-methylbutenoic acids, for example. In view of the requirements of apossible continuous implementation of the process, the amounts of thesecompounds present can reach up to 90% by weight of the reaction mixturecharged to the hydroxycarbonylation reaction.

The concentration of butadiene is a significant reaction parameter, inparticular as regards the stability of the palladium catalyst, that isto say essentially its maintenance in solution in the reaction mixture.It has thus been observed that it is unfavourable to have less than 0.2%by weight of butadiene with respect to the total weight of the reactionmixture. Preferably, when the reaction is carried out batchwise, theconversion of the butadiene or its derivatives will be limited so thatthe reaction mixture includes at least 0.5% by weight of the saidbutadiene or its derivatives.

The concentration of butadiene will also preferably be maintained at avalue of less than or equal to 50% as weight by weight of the reactionmixture and more preferably still at a value of equal to or less than30%, when the reaction is carried out in a batchwise process, and at avalue of equal to or less than 10%, when the reaction is carried out ina continuous process.

The embodiment of the hydroxycarbonylation process described aboveexhibits the advantage, with respect to other embodiments, of keepingthe palladium in solution in the reaction medium up to the end of thereaction, making it possible to maintain high kinetics.

The hydroxycarbonylation reaction can be carried out at a temperaturegenerally situated between 60° C. and 230° C. and preferably between 90°C. and 200° C. and under a pressure, at the temperature, of 50 to 500bar and preferably from 100 to 300 bar.

The carbon monoxide partial pressure, measured at 25° C., is from 25 barto 440 bar and preferably from 55 bar to 240 bar.

As has been indicated, the process of the invention can be carried outcontinuously or batchwise. There will therefore be good reason to adjustthe various operating conditions defined above according to theimplementation chosen.

The reaction medium obtained at the end of the hydroxycarbonylationreaction comprises palladium in the dissolved form.

The invention provides a treatment of this reaction medium which makesit possible to recover palladium in the insoluble form with a degree ofrecovery of approximately 100%.

This treatment consists, in a first stage, in extracting the carbonmonoxide dissolved in the reaction medium. This extraction can beobtained by heating the medium with an atmosphere not comprising CO.More advantageously, this extraction is carried out by placing thereaction medium under an inert or hydrogen atmosphere, optionally withsparging of this inert gas or hydrogen into the reaction medium. Theterm “inert gas” is understood to mean nitrogen or the rare gases.

This stage can be carried out at a temperature of between 20° C.(ambient temperature) and 150° C.

This operation is carried out to extract virtually all the carbonmonoxide which can be extracted from the reaction medium. Thus, theconcentration of carbon monoxide in the reaction medium canadvantageously be less than 600 ml/l, preferably less than 100 ml/l, ofsolution. Advantageously, the concentration of CO in the reaction mediumis between 0.001 ml/l and 600 ml/l.

After extraction of the carbon monoxide, the process of the inventioncomprises a stage of reduction of the dissolved palladium, generally inthe 2+ oxidation state, to palladium in the zero oxidation state(Pd(0)). This palladium is separated from the reaction medium by theusual liquid/solid separating techniques, such as filtration, separationby settling, centrifugation, distillation or evaporation of the liquidmedium.

According to a preferred embodiment of the invention, a compound whichis insoluble in the reaction medium is present in the said medium beforethe precipitation of the Pd(0).

This insoluble compound can be added to the reaction medium at any time,for example at the beginning of the hydroxycarbonylation process, at theend of the latter or immediately before the stage of reduction of thepalladium.

This insoluble compound is advantageously added before the beginning ofthe hydroxycarbonylation reaction.

According to the invention, the palladium in the zero oxidation stateprecipitates and is deposited on or in the heterogeneous phase composedof this insoluble compound, thus facilitating its extraction and itsseparation from the reaction medium.

Generally, this insoluble compound should not have an effect on thehydroxycarbonylation reaction, in particular should not influence thecatalytic effect of the palladium or the selectivity of the reaction.

Mention may be made, as insoluble compounds which are suitable for theinvention, of inorganic compounds which are advantageously porous orwhich exhibit a large specific surface area. Mention may be made, inthis family of compounds, as examples, of active charcoals, alumina,silica, zirconia, cerium oxide or more generally rare earth metaloxides.

Mention may be made, as other insoluble compounds which are suitable forthe invention, of polymer foams, such as polystyrene foams, or siliconeoils.

The amount of insoluble compounds added is not critical and can varywithin wide limits.

According to one characteristic of the invention, the stage of reductionof the palladium to the zero oxidation state is carried out by placingthe reaction medium under a hydrogen atmosphere.

However, it is also possible, without departing from the scope of theinvention, to add a reducing compound to the medium, such asborohydrides, such as NaBH₄, for example, or metal hydrides.

This reducing stage can be carried out between ambient temperature (20°C.) and 150° C. and at a hydrogen pressure of between 1 bar and 100 bar.

However, in an embodiment which makes it possible to reduce thepalladium to the zero oxidation state without affecting the unsaturationor unsaturations present in the hydrocarbonyl compound, the temperatureof the reducing stage is advantageously between 20° C. (ambienttemperature) and 80° C.

In the other embodiment, with a temperature of between 80° C. and 150°C., the unsaturations of the. carboxylic acid obtained byhydrocarbonylation can be hydrogenated to obtain a saturated carboxylicacid. The process of the invention thus makes it possible, starting frombutadiene, to produce pentanoic acid.

The process of the invention makes it possible to recover all thepalladium present in the reaction medium.

In addition, the insoluble compound comprising the palladium can betreated with acids to redissolve the palladium and to make it possibleto recycle it in a further hydroxycarbonylation stage.

The process of the invention thus makes it possible to implement thereactions for the hydroxycarbonylation of unsaturated compounds withcatalysis with palladium without loss of catalyst. Such a process canthus be operated economically.

The invention will be more fully illustrated by the examples givenbelow, which are solely by way of illustration and without limitingeffect.

EXAMPLE 1

The following are charged to a glass flask:

3-Pentenoic acid (90% 10.0 g purity) Butadiene 2.7 g (50 mmol)Chlorobutene 0.3 g (0.35 mmol) Water 0.9 g (50 mmol)Palladium-on-active- 0.71 g charcoal (3%)

This Pd/C catalyst is sold by Engelhard under the trade name Escat 1625207.

The glass flask is introduced into a 125 ml autoclave. The latter isimmediately pressurized to 100 bar of CO at ambient temperature. Theautoclave is placed in an oven and the mixture is heated to 140° C.while shaking. When the preset temperature is reached, the CO pressureis raised to 200 bar with connection to a source of CO to maintain aconstant pressure. The CO consumption is estimated with respect to thedifference in pressure measured in the source.

After reacting for 40 minutes, corresponding to a degree of conversion(DC) of the butadiene of 63%, the autoclave is cooled in a water bath to20° C. and then degassed. Three purges with hydrogen are carried outunder a pressure of 20 bar of hydrogen. The CO content in the medium is0.6 ml of CO per litre of solution.

A pressure of 20 bar of hydrogen is applied and the mixture is heated at80° C. with stirring for one hour (phase of reduction of the palladium).After cooling and degassing, the reaction medium is filtered. Thecharcoal collected is dried before analysis.

The reaction mass collected after filtration is analysed by liquidchromatography (HPLC) and gas chromatography (GC).

The following results were obtained:

CY (3-pentenoic acid)=92%

CY (diacids)=4.6%

CY (2-methyl-3-butenoic acid)=2.9%.

CY (pentanoic acid)=0.07%

Quantitative determination of the palladium on the charcoal collectedand in the reaction mass after filtration is carried out by ICP-OES orICP-MS. The results show that 98% of the palladium charged to thereaction is recovered on the charcoal and 1% is found in the dissolvedform in the reaction medium.

The term “degree of conversion (DC) of the butadiene” should beunderstood as meaning the ratio, expressed as %, of the number of molesof butadiene which have disappeared to the number of moles of butadienecharged.

The term “CY” should be understood as meaning the selectivity for theproduct X indicated corresponding to the ratio, expressed as %, of thenumber of moles of product X formed to the number of theoretical molesof product X calculated for the number of moles of butadiene converted.

EXAMPLE 2

The following are charged to a glass flask:

3-Pentenoic acid (90% 10.0 g purity) Butadiene 2.6 g Chlorobutene 0.15 gWater 0.9 g Palladium acetate 0.10 g Charcoal, Ceca L3S 1.1 g

The charcoal is sold by Ceca.

The glass flask is introduced into a 125 ml autoclave. The latter isimmediately pressurized to 100 bar of CO at ambient temperature. Theautoclave is placed in an oven and the mixture is heated to 140° C.while shaking. When the preset temperature is reached, the CO pressureis brought to 200 bar and the autoclave is placed in communication witha source of CO to maintain a constant pressure. The CO consumption isestimated with respect to the difference in pressure measured in thesource.

After reacting for 19 minutes, corresponding to a DC of the butadieneequal to 65%, the autoclave is cooled in a water bath to 20° C. and thendegassed. Two purges with hydrogen are carried out under 20 bar ofhydrogen. The solution obtained comprises 40 ml of CO per litre ofsolution.

A pressure of 20 bar of hydrogen is applied and the mixture is heated at40° C. with stirring for fifteen minutes. After cooling and degassing,the reaction medium is filtered. The charcoal recovered is dried beforeanalysis. The reaction mass is analysed by high performance liquidchromatography (HPLC) and gas chromatography (GC).

The following results were obtained:

CY (3-pentenoic acid)=83%

CY (diacids)=11%

CY (2-methyl-3-butenoic acid)=3.6%

CY (pentanoic acid)=1.8%

Quantitative determination of the palladium on the charcoal collectedand in the reaction mass after filtration is carried out by ICP-OES orICP-MS. The results show that 1% of the palladium charged to thereaction its found in the dissolved form in the reaction medium, theremainder being recovered on the charcoal.

EXAMPLE 3

The following are charged to a glass flask:

3-Pentenoic acid (90% 10.0 g purity) Butadiene 3.2 g Chlorobutene 0.32 gWater 0.9 g Palladium acetate 0.10 g Charcoal, Ceca L3S 1.0 g

The charcoal is sold by Ceca.

The glass flask is introduced into an 125 ml autoclave. The latter isimmediately pressurized to 100 bar of CO at ambient temperature. Theautoclave is placed in an oven and the mixture is heated to 140° C. withshaking. When the preset temperature is reached, the CO pressure isbrought to 200 bar and the autoclave is placed in communication with asource of CO to maintain a constant pressure. The CO consumption isestimated with respect to the difference in pressure measured in thesource.

After reacting for 23 minutes, corresponding to a DC of the butadieneequal to 70%, the autoclave is cooled in a water bath to 20° C. Theautoclave is reduced in pressure and placed under a pressure of 60 barwith an H₂/CO mixture with a 95/5 content by weight. The autoclave isheated at 40° C. for 45 minutes. After cooling and degassing, thereaction mixture is filtered. The charcoal recovered is dried beforeanalysis. The reaction mass is analysed by high performance liquidchromatography (HPLC) and gas chromatography (GC).

The following results were obtained:

CY (3-pentenoic acid)=87%

CY (diacids)=10%

CY (pentanoic acid)=0.25%

CY (2-methyl-3-butenoic acid)=3.2%

Quantitative determination of the palladium on the charcoal collectedand in the reaction mass after filtration is carried out by ICP-OES orICP-MS. The results show that only 34% of the palladium charged to thereaction is recovered on the charcoal and 62% is found in the dissolvedform in the reaction medium.

EXAMPLE 4

The following are charged to a glass flask:

3-Pentenoic acid (90% 10.2 g purity) Butadiene 2.7 g Chlorobutene 0.20 gWater 0.9 g Palladium-on-active- 1.0 g charcoal (3%)

This Pd/C catalyst is sold by Engelhard under the trade name Escat 1625207

The glass flask is introduced into a 125 ml autoclave. The latter isimmediately pressurized to 100 bar of CO at ambient temperature. Theautoclave is placed in an oven and the mixture is heated to 140° C. withshaking. When the preset temperature is reached, the CO pressure isbrought to 200 bar and the autoclave is placed in communication with asource of CO to maintain a constant pressure. The CO consumption isestimated with respect to the difference in pressure measured in thesource.

After reacting for 24 minutes, corresponding to a DC of the butadieneequal to 51%, the autoclave is cooled in a water bath to 20° C. and thenslowly degassed. No purging is carried out, the CO concentration being1000 ml of CO per litre of solution. A pressure of 20 bar of hydrogen isthen applied and the mixture is heated at 40° C. with stirring forfifteen minutes. After cooling and degassing, the reaction medium isfiltered. The charcoal recovered is dried before analysis. The reactionmass is analysed by high performance liquid chromatography (HPLC) andgas chromatography (GC).

The following results were obtained:

CY (3-pentenoic acid)=87%

CY (diacids)=10%

CY (pentanoic acid)=0.3%

Quantitative determination of the palladium on the charcoal collectedand in the reaction mass after filtration is carried out by ICP-OES orICP-MS. The results show that 88% of the palladium charged to thereaction is found in the dissolved form in the reaction medium.

EXAMPLE 5

The following are charged to a glass flask:

3-Pentenoic acid (90% 10.0 g purity) Butadiene 2.7 g Chlorobutene 0.30 gWater 0.9 g Palladium acetate 0.11 g Charcoal, Ceca L3S 1.0 g

The glass flask is introduced into a 125 ml autoclave. The latter isimmediately pressurized to 100 bar of CO at ambient pressure. Theautoclave is placed in an oven and the mixture is heated to 140° C. withshaking. When the preset temperature is reached, the CO pressure isbrought to 200 bar and the autoclave is placed in communication with asource of CO to maintain a constant pressure. The CO consumption isestimated with respect to the difference in pressure measured in thesource.

After reacting for 14 minutes, corresponding to a DC of the butadieneequal to 64%, the autoclave is cooled in a water bath to 20° C. and thenslowly degassed. No purging is carried out. A pressure of 20 bar ofhydrogen is then applied and the mixture is heated at 80° C. withstirring for fifteen minutes. After cooling and degassing, the reactionmedium is filtered. The charcoal recovered is dried before analysis. Thereaction mass is analysed by high performance liquid chromatography(HPLC) and gas chromatography (GC).

The following results were obtained:

CY (3-pentenoic acid)=80%

CY (diacids)=15%

CY (pentanoic acid)=0.2%

CY (2-methyl-3-butenoic acid)=3.8%

Quantitative determination of the palladium on the charcoal collectedand in the reaction mass after filtration is carried out by ICP-OES orICP-MS. The results show that 80% of the palladium charged to thereaction is found in the dissolved form in the reaction medium.

EXAMPLE 6

The following are charged to a glass flask:

3-Pentenoic acid (90% 10.0 g purity) Butadiene 2.6 g Chlorobutene 0.30 gWater 0.91 g Palladium acetate 0.10 g Charcoal, Ceca L3S 1.0 g

The glass flask is introduced into a 125 ml autoclave. The latter isimmediately pressurized to 100 bar of CO at ambient pressure. Theautoclave is placed in an oven and the mixture is heated to 140° C. withshaking. When the preset temperature is reached, the CO pressure isbrought to 200 bar and the autoclave is placed in communication with asource of CO to maintain a constant pressure. The CO consumption isestimated with respect to the difference in pressure measured in thesource.

At the end of the reaction, the autoclave is cooled in a water bath to20° C. and then slowly degassed. Purging is carried out with 40 bar ofhydrogen and the CO concentration falls to 40 ml of CO per litre ofsolution. A pressure of 20 bar of hydrogen is then applied and themixture is heated at 40° C. with stirring for fifteen minutes. Aftercooling and degassing, the reaction medium is filtered. The charcoalrecovered is dried before analysis. The reaction mass is analysed byhigh performance liquid chromatography (HPLC) and gas chromatography(GC).

The following results were obtained:

CY (3-pentenoic acid)=80%

CY (diacids)=12%

CY (pentanoic acid)=2.1%

CY (2-methyl-3-butenoic acid)=3.9%

Quantitative determination of the palladium on the charcoal collectedand in the reaction mass after filtration is carried out by ICP-OES orICP-MS. The results show that 1% of the palladium charged to thereaction is found in the dissolved form in the reaction medium.

EXAMPLE 7

The following are charged to a glass flask:

3-Pentenoic acid (90% 10.0 g purity) Butadiene 2.8 g Chlorobutene 0.31 gWater 0.9 g Palladium acetate 0.10 g Charcoal, Ceca L3S 1.0 g

The charcoal is sold by Ceca.

The glass flask is introduced into a 125 ml autoclave. The latter isimmediately pressurized to 100 bar of CO at ambient temperature. Theautoclave is placed in an oven and the mixture is heated to 140° C. withshaking. When the preset temperature is reached, the CO pressure isbrought to 200 bar and the autoclave is placed in communication with asource of CO to maintain a constant pressure. The CO consumption isestimated with respect to the difference in pressure measured in thesource.

At the end of the reaction, the autoclave is cooled in a water bath to20° C. The autoclave is reduced in pressure, then three purges withhydrogen are carried out under 20 bar of hydrogen (the CO concentrationfalling to 0.6 ml per litre of solution), then a pressure of 10 bar ofhydrogen is applied and the mixture is heated at 80° C. with stirringfor five minutes. After cooling and degassing, the reaction medium isfiltered. The charcoal recovered is dried before analysis. The reactionmass is analysed by high performance liquid chromatography (HPLC) andgas chromatography (GC).

The following results were obtained:

CY (3-pentenoic acid)=81%

CY (4-pentenoic acid)=3.7%

CY (diacids)=8.5%

CY (2-methyl-3-butenoic acid)=3.3%

CY (pentanoic acid)=4.4%

Quantitative determination of the palladium on the charcoal collectedand in the reaction mass after filtration is carried out by ICP-OES orICP-MS. The results show that 97% of the palladium charged to thereaction is recovered on the charcoal and 1% is found in the dissolvedform in the reaction medium.

EXAMPLE 8

The following are charged to a glass flask:

3-Pentenoic acid (90% 10.0 g purity) Butadiene 2.7 g Chlorobutene 0.30 gWater 0.95 g Palladium acetate 0.10 g Alumina, Degussa 1.0 g type C

The glass flask is introduced into a 125 ml autoclave. The latter isimmediately pressurized to 100 bar of CO at ambient temperature. Theautoclave is placed in an oven and the mixture is heated to 140° C. withshaking. When the preset temperature is reached, the CO pressure isbrought to 200 bar and the autoclave is placed in communication with asource of CO to maintain a constant pressure. The CO consumption isestimated with respect to the difference in pressure measured in thesource.

At the end of the test, the autoclave is cooled in a water bath to 20°C. and then degassed. Three purges with hydrogen are carried out under20 bar of hydrogen (the CO concentration falling to 0.6 ml per litre ofsolution), then a pressure of 20 bar of hydrogen is applied and themixture is heated at 80° C. with stirring for forty-five minutes. Aftercooling and degassing, the reaction medium is filtered. The aluminarecovered is dried before analysis.

Quantitative determination of the palladium on the alumina collected andin the reaction mass after filtration is carried out by ICP-OES orICP-MS. The results show that 97% of the palladium charged to thereaction is recovered on the alumina and less than 0.05% is found in thedissolved form in the reaction medium.

EXAMPLE 9

1) Preparation of the π-crotyl-Pd Chloride Complex

5.04 g of PdCl₂, 3.37 g of NaCl, 50 cm³ of methanol, 15 cm³ of water,8.03 g of crotyl chloride and a further 20 cm³ of methanol aresuccessively charged to a 150 cm³ round-bottomed glass flask.

The heterogeneous mixture is stirred and becomes gradually dark brownand cloudy. The solution is subsequently treated with stirring with agentle stream of carbon monoxide (bubble by bubble) for one hour. Themixture becomes clearer and a yellow precipitate appears. The stirringand the stream of CO are halted, the solution is left standing for onehour and then it is poured into 300 cm³ of water and extracted with 5times 50 cm³ of chloroform. The resulting straw-yellow organic phase iswashed with 2 times 100 cm³ of water and dried over disodium sulphateovernight, and then the solvent is evaporated. 3.35 g of a pale yellowsolid are thus recovered, the solid having a purity of greater than 94%(quantitative determination by Nuclear Magnetic Resonance: NMR).

2) Hydroxycatbonylation of Chlorobutene

The following are charged to a glass flask:

Chlorobutene 5.0 g Chlorocrotyl palladium 10.3 mg

The glass flask is introduced into a 125 ml autoclave. The latter isimmediately pressurized to 100 bar of CO at ambient temperature. Theautoclave is placed in an oven and the mixture is heated to 130° C. withshaking. When the preset temperature is reached, the CO pressure isbrought to 200 bar and the autoclave is placed in communication with asource of CO to maintain a constant pressure.

After 60 minutes, the autoclave is cooled in a water bath to 20° C. andthen degassed. The homogeneous reaction mass is analysed by highperformance liquid chromatography (HPLC) and gas chromatography (GC).

The following results were obtained:

RY (P3)=12.7%

RY (P2)=4.4%

The remainder is very predominantly chlorobutene.

2.09 g of the solution thus obtained are placed in a glass flask and 95mg of Ceca L3S charcoal are added. Two purges under 15 bar of hydrogenare carried out and the mixture is shaken under 20 bar of H₂ and heatedto 80° C. Once the temperature has been reached, a pressure of 40 bar ofhydrogen is applied for 60 minutes. The autoclave is degassed and thereaction medium is filtered.

Quantitative determination of the palladium on the charcoal collectedand in the reaction mass after filtration is carried out by ICP-OES orICP-MS. The results show that 100% of the palladium charged to thereaction is recovered on the charcoal.

EXAMPLE 10

The following are charged to a glass flask:

Pentanoic acid 10.0 g Butadiene 2.6 g Chlorobutene 0.30 g Water 0.92 gPalladium acetate 0.11 g Charcoal, Ceca L3S 1.0 g

The glass flask is introduced into a 125 ml autoclave. The latter isimmediately pressurized to 100 bar of CO at ambient temperature. Theautoclave is placed in an oven and the mixture is heated to 140° C. withshaking. When the preset temperature is reached, the CO pressure isbrought to 200 bar and the autoclave is placed in communication with asource of CO to maintain a constant pressure. The CO consumption isestimated with respect to the difference in pressure measured in thesource.

At the end of the reaction, the autoclave is cooled in a water bath to20° C. and then slowly degassed. Five purges are carried out under 60bar of hydrogen (the CO concentration falling to 0.05 ml per litre ofsolution). The mixture is then heated at 140° C. under 70 bar ofhydrogen with stirring for thirty-five minutes. After cooling anddegassing, the reaction medium is filtered. The charcoal recovered isdried before analysis. The reaction mass is analysed by high performanceliquid chromatography (HPLC) and gas chromatography (GC).

The following results were obtained:

CY (pentanoic acid)=93%

CY (diacids)=3.0%

CY (2-methyl-3-butanoic acid)=3.9%

Quantitative determination of the palladium on the charcoal collectedand in the reaction mass after filtration is carried out by ICP-OES orICP-MS. The results show that nearly 100% of the palladium charged tothe reaction is recovered on the charcoal, 0.025% being found in thedissolved form in the reaction medium.

1. Process for the preparation of unsaturated or saturated carboxylicacids from compounds comprising an ethylenic or acetylenic unsaturationconjugated with an other unsaturation or an electron-donating group byhydroxycarbonylation reaction with carbon monoxide and water in thepresence of a palladium-based catalyst in a reaction medium, whichcomprises (1) treating the reaction medium comprising said unsaturatedor unsaturated carboxylic acids, byproducts, and water, after the end ofthe hydroxycarbonylation reaction, with a gas to extract carbon monoxidefrom the reaction medium to obtain a CO concentration in the reactionmedium of less than 600 ml of CO per litre, (2) treating the reactionmedium with hydrogen to reduce the palladium to the zero oxidationstate, and (3) separating precipitated palladium from the reactionmedium.
 2. Process according to claim 1, wherein the concentration ofcarbon monoxide in the reaction medium before the stage of treatmentwith hydrogen is less than 10 mmol/1.
 3. Process according to claim 2,wherein the concentration of carbon monoxide in the reaction mediumbefore the stage of treatment with hydrogen is between 0.001 ml/l and600 ml/l.
 4. Process according to claim 1, wherein the gas forentrainment of the carbon monoxide is selected from the group consistingof nitrogen, the rare gases and hydrogen.
 5. Process according to claim1, wherein the stage of reduction of the palladium to the zero oxidationstate is carried out under a hydrogen pressure of between 1 bar and 100bar.
 6. Process according to claim 1, wherein the stage of reduction ofthe palladium to the zero oxidation state is carried out at atemperature of between 20° C. and 150° C.
 7. Process according to claim1, wherein a compound which is insoluble in the reaction medium is addedto the said medium and then separated from the said medium after thestage of reduction of the palladium to the zero oxidation stage. 8.Process according to claim 7, wherein the compound which is insoluble inthe reaction medium is selected from the group consisting of activecharcoals, alumina, silica, zirconia, cerium oxide, polystyrene foamsand silicone oils.
 9. Process according to claim 7, wherein the compoundwhich is insoluble in the reaction medium is added at the beginning ofthe reaction.
 10. Process according to claim 7, wherein the compoundwhich is insoluble in the reaction medium is added before the stage ofreduction of the palladium.
 11. Process according to claim 1, whereinthe compounds comprising a conjugated ethylenic unsaturation areselected from the group consisting of diolefins, allyl alcohols, allylethers, allyl esters and allyl halides.
 12. Process according to claim11, wherein the diolefin is butadiene.
 13. Process according to claim 7,wherein the palladium deposited on the insoluble compound is recoveredby treatment of the said insoluble compound after separation from thereaction medium.
 14. Process according to claim 13, wherein thetreatment of the insoluble compound comprising the reduced palladium isa dissolution of the palladium by attack by a strong acid.